Hydrogen is Safe
Hydrogen inherently poses no more danger than other conventional fuels, such as gasoline or natural gas. Here are some facts about hydrogen:
Hydrogen is non-toxic, non-poisonous, and will not contaminate groundwater. A release of hydrogen into the air will not contribute to atmospheric pollution.
Hydrogen is 14 times lighter than air and rises at 20 meters per second, which means that it diffuses extremely rapidly. Due this high buoyancy, when released into the air, hydrogen quickly diffuses into a non-flammable concentration.
When compared to hydrocarbon fires, hydrogen fires have much lower levels of radiant heat, greatly reducing the risk of secondary fires.
Hydrogen needs oxygen to burn, meaning that combustion within a hydrogen tank is impossible. In event of a leak, the physical properties of hydrogen would force the gas to quickly diffuse and rise, moving the gas away from the leak.
Because liquid hydrogen must be stored at extremely cold temperatures (below -423 degrees Fahrenheit), today’s storage containers are double-walled, vacuum-jacketed, superinsulated, and designed to vent hydrogen safely in gaseous form if a breach of either the outer or inner wall is detected.
It is interesting to compare the flammability range for common gases and fuels. Flammability range is denoted by the lower and upper flammability limits (LFL and UFL respectively) by volume, beyond which the mixture is not flammable. Gasoline vapor has a LFL of about 1.4%, whereas natural gas (methane) and hydrogen have similar LFLs of about 4%. The upper limit varies considerably between these fuels with gasoline at about 7.6%, natural gas (methane) at about 15% and hydrogen at about 75%. While the LFL for hydrogen is above gasoline and at similar values for other common fuels its UFL is significantly higher giving hydrogen a very wide flammability range. Since most often a pure hydrogen source is mixed with the oxidizer (air) creating a lean to rich mixture where the hydrogen mixes with the oxidizer we are usually more interested in the lean limit from a safety perspective. Hydrogen is also very buoyant; this property modifies its flame properties. The LFL for hydrogen actually depends on the flame propagation direction. The commonly quoted value of 4% is for an upward propagating flame and is the lowest value. However, hydrogen flames will not propagate in any other direction until the mixture reaches 8 – 10%. Fuel LFL (% by Volume) UFL (% by Volume) Gasoline 1.4 7.6 Natural Gas (Methane) 5 15 Hydrogen (Upward Propagating) 4 75 Hydrogen (Downward, Horizontal) 8-10% 75% (reference - http://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html).
As of June 2012, the United States safely produces and uses over 9 million tons of hydrogen per year. Standards and regulations have been set to ensure the safe production, storage, handling, and use of hydrogen. All hydrogen components undergo strict third-party testing for safety and structural integrity.
|The Fuel Cell - 14th Forum for Producers and Users (f-cell)|
|October 6 - 8, 2014 | Stuttgart, Germany|
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|April 26-29, 2015 | San Diego, California|